Radiological Characteristics of Carbonated Portland Cement Mortars Made with GGBFS

The objective of this study is to assess whether the carbonation process can modify the physicochemical characteristics of the natural radionuclides of the three natural radioactive series, together with K-40. Three mortar specimens with different percentages of ground granulated blast-furnace slag (GGBFS), cured under water for 1, 3, 7, 14, or 28 days, were subjected to a natural carbonation process. Activity concentrations for the solid and ground mortars were determined by gamma spectrometry and by radiochemical separation of isotopic uranium. The novelty of this paper relies principally on the study we have carried out, for the first time, of the radiological characteristics of carbonated Portland cement mortars. It was found that the chemical properties of the 3 mortar specimens were not affected by the carbonation process, with particular attention placed on uranium (U-238, U-235, and U-234), the activity concentrations of which were equivalent to the Ra-226 results and ranged from 5.5 +/- 1.6 Bq kg(-1) to 21.4 +/- 1.2 Bq kg(-1) for the U-238. The average activity concentrations for the 3 types of mortars were lower than 20.1 Bq kg(-1), 14.5 Bq kg(-1), and 120.2 Bq kg(-1) for the Ra-226, Th-232 (Pb-212), and K-40, respectively. Annual effective dose rates were equivalent to the natural background of 0.024 mSv. In addition, it was observed that the variation rate for the Rn-222 emanation was due primarily to the Portland cement hydration and not due to the pore size redistribution as a consequence of the carbonation process. This research will provide new insights into the potential radiological risk from carbonated cement-based materials. Moreover, the assessment that is presented in this study will convey valuable information for future research that will explore the activity concentration of building materials containing NORM materials.

Automated summary

The study assesses the impact of the carbonation process on natural radionuclides. The results indicate that the carbonation process does not affect the chemical properties of the mortar and the activity concentrations of the radionuclides are relatively low, with annual effective dose rates equivalent to the natural background level.